The present invention relates to front derailleurs for bicycles and more particularly to a front derailleur including a chain guide configured to minimize shifting noises.
A bicycle derailleur, in particular a front derailleur, shifts a bicycle chain from one chainring to an adjoining chainring. This shifting operation is initiated by a shifting motion of the chain cage or chain guide that runs transverse to the travel direction of the chain. The shifting operation may occur in both directions from a larger chainring to a next smaller chainring or from a smaller chainring to a next larger chainring. The chain runs between inner and outer guide plates of the chain guide and, depending on the desired shifting direction, is shifted by either the inner or outer guide plate to the adjoining chainring. These guide plates each have interior surfaces facing the chain adapted to the respective shifting directions.
EP 1 314 636 A2 discloses a chain guide or a chain cage having inner and outer guide plates. The chain is disposed between the guide plates and includes inner and outer links connected by link pins. An interior surface of the outer guide plate protrudes inwardly to form a guide surface that has upper, middle, and lower regions with different shapes and offsets. The upper region of the guide surface contacts the chain when it is shifted from a larger chainring to a middle chainring. The lower region is used when shifting the chain from the middle chainring to a smaller chainring. The lower, middle, and upper regions of the guide surface have different offsets causing shifting noises when the chain grazes across them during shifting operations. The guide surface has a relatively narrow width for contacting the chain, when viewed in the direction of the chain travel. When the narrow-width guide surface comes into contact with the chain and dips into the gap between the outer chain links, shifting noises result. These shifting noises also occur in many other chain guide configurations.